1. Field of the Invention
This application is based on patent applications Nos. 2002-006194 and 2002-006168 filed in Japan, the contents of which are incorporated herein by reference.
The present invention is taken advantage of in a packet communication network in which, at each node, link state information which indicates the state of the links by which other nodes are connected to the current node is advertised to the other nodes, and, in each node, a link cost is determined according to the link state information which is included in these advertisements, and a path is calculated according to this link cost which has thus been determined.
Furthermore, the present invention is taken advantage of in a packet communication network which combines packet switch processing in which packet switching is performed by IP address units, and wavelength path switch processing in which wavelength path switching is performed by wavelength units.
2. Description of the Related Art
FIG. 9 shows a packet communication network which is provided with a link state type routing protocol. FIG. 10 shows the structure of a node in a conventional communication network. FIG. 11 shows an example of a link state database (DB) in a conventional communication network.
Open Shortest Path First (OSPF) is one routing protocol in an Internet Protocol (IP) communication network (refer to J. Moy, “OSPF Version 2”, RFC 2328, 1998). In OSPF, a node which is connected to a link manages the state of the link, and the state of this link is advertised within the network as link state information. A protocol which is performed for routing based upon this type of link state is termed a link state type routing protocol.
Various parameters may be used as the state of the link, such as, as shown in FIG. 11, the presence or absence of a link between the two nodes, link capacity, the bandwidth which is reserved for the link, fixed cost, or the like. For example, the fixed cost is set so as to be proportional to the distance of the link. In OSPF, it is possible to advertise this link state information (refer to J. Moy, “OSPF Version 2”, RFC 2328, 1998, and R. Coltun, “The OSPF Opaque LSA Option”, RFC 2370, 1998).
As shown in FIG. 10, each node comprises a routing control section 6. This routing control section 6 comprises a link state database 4, a flooding section 10, a path calculation section 3, and a routing table 7. The link state of the current node is notified to the link state database 4, and the link state database 4 is updated thereby. This updated link state is advertised via the flooding section 10 to the other nodes which are connected to the current node as link state information.
Furthermore, along with updating the link state database 4 of the current node with link state information which has been advertised from other nodes, the link state information is further advertised towards yet other nodes. By advertising this link state information, the link state information is propagated to all the nodes within the communication network, and it is possible to ensure that each node maintains the same link state database 4.
Path calculation based upon the link state database 4 is performed by the path calculation section 3, and the routing table 7 is updated.
Here, by way of example, a method for calculating the path for the packets of the best effort class will be discussed. It is possible to calculate the bandwidth which is not reserved for the link (the non reserved bandwidth) by calculating the difference between the capacity of the link and the reserved bandwidth. If the non reserved bandwidth of a link is less than or equal to a threshold value which is set in advance, this link is excluded from the candidates of the link used in path calculation, since the non reserved bandwidth is insufficient. From the candidates for the link to be used, the fixed cost is taken as the distance of the link, and the shortest path from the current node to each arrival node is selected. Based upon the result thereof, the destination of the current hop is determined, and is reflected in the routing table 7. This method is one which aims at the beneficial result of minimizing this packet forwarding delay time between the ends of the link, under the condition that there is a constraint upon the packet forwarding delay time between the ends of the link. The delay time exerts an influence upon the bandwidth which can be utilized and upon the distance of the link.
Furthermore, another method for calculating the path for the packets of the best effort class will be discussed. It is possible to calculate the bandwidth which is not reserved for the link (the non reserved bandwidth) from the capacity of the link and the reserved bandwidth. The reciprocal of the non reserved bandwidth is taken as the distance of the link, and the shortest path from the current node to each arrival node is selected. Based upon the result thereof, the destination of the current hop is determined, and is reflected in the routing table 7. This method is one which aims at the beneficial result of minimizing the packet forwarding delay time between the ends of the link.
However, it may happen that the reserved bandwidth or the fixed cost does not reflect the actual state of the link. In other words, the problem may arise that it is not possible to utilize the network resources efficiently, because the amount of traffic which is being transmitted upon the link is always varying, and the reserved bandwidth or the fixed cost does not necessarily reflect the situation with the link which is being used at the moment.
This problem will be further explained with reference to the conventional packet communication network which is shown in FIGS. 25 through 27. FIG. 25 is a figure showing a conventional packet communication network. FIGS. 26A through 26C are figures showing a classification of switching functions. FIG. 27 is a block structure diagram of a router upon this conventional packet communication network.
As shown in FIG. 25, nodes having three types of switching function are disposed upon the communication network, and these nodes are connected together by optical fibers. FIG. 26A shows a node which is endowed with a packet-based switching function (PSC: Packet Switch Capable). This will herein be termed a router. FIG. 26B shows a node which is endowed with a wavelength-based switching function (LSC: Lambda Switch Capable). This will herein be termed an optical cross-connect. FIG. 26C shows a node which is endowed both with a packet-based switching function and also a wavelength-based switching function (PSC+LSC). This will herein be termed an optical router. With such an optical router, depending upon its setting, either only wavelength-based switching is performed, or both wavelength-based switching and also packet-based switching are performed.
In FIG. 25, optical paths are established between the router A and the optical router C, between the optical router C and the router F, and between the router C and the router E. These optical paths are terminated by the routers. Optical path do not terminate at the optical cross-connects B, D, and G, and they only perform wavelength-based switching.
The flow of packets from the router A to the router F will now be considered. As one scheme for forwarding the packets, there is a scheme of establishing an electrical path which operates between grounds utilizing electrical levels. Furthermore, there is a scheme of establishing a routing up to the destination by referring to the routing tables which are held in the routers, based upon the header information in the packets, rather than by setting an electrical path between grounds. Both the conventional techniques and the technique of the present invention can be applied both to a scheme in which an electrical path is established, and to a scheme in which no electrical path is established. Herein, the scheme will be discussed in which an electrical path is established between grounds.
The electrical path from the router A to the router F is terminated by the router A and the router F, and is not terminated by the optical router C. This electrical path from the router A to the router F uses two optical paths and arrives at the router F by way of the optical cross-connect B->the optical router C->the optical cross-connect D. Furthermore, the electrical path from the router A to the router E is terminated by the router A and the router E, and is not terminated by the optical router C. This electrical path from the router A to the router E uses two optical paths and arrives at the router E by way of the optical cross-connect B->the optical router C->the optical cross-connects B and G. Furthermore, an electrical path between A and C is established for traffic between the grounds A and C. The optical path between the nodes A and C includes the electrical paths between the grounds A and F, between the grounds A and C, and between the grounds A and E.
With a conventional packet communication network, in order to change the establishment of the optical paths and the electrical paths as in FIG. 25, the maintainer issues commands to an integrated control section 20A for establishing such changes of the electrical paths or of the optical paths. By doing this, establishment change signals are transmitted from the integrated control section 20A to each of the nodes, and each of the nodes starts the establishment of an electrical path or of an optical path, according to these signals.
As shown in FIG. 27, a path change request reception section 7 receives a request for establishment change of an electrical path or of an optical path from the integrated control section 20A, and, based upon the information in the link state database 4A, a path which satisfies the path change request by the path calculation section 3A is sought out, and, if such a path has been found, a signal for establishing an electrical path or an optical path is dispatched by a path establishment section 5A to the downstream nodes.
Updating of the link state database 4A is performed according to the following Open Shortest Path First (OSPF), which is one routing protocol for a communication network which employs Internet Protocol (IP). With OSPF, a node which is connected to a link manages the state of the link, and advertises the state of this link over the network (refer to J. Moy, “OSPF Version 2”, RFC 2328, 1998, and R. Coltun, “The OSPF Opaque LSA Option”, RFC 2370, 1998). Furthermore, there is a type of OSPF in which OSPF upon an IP network has been extended to the optical layer (refer to A. Banerjee, J. Drake, J. P. Lang, B. Turner, K. Kompella, and Y. Rekhter, “Generalized Multiprotocol Label Switching: An Overview of Routing and Management Enhancements”, IEEE Commun. Mag., pp. 144-150, January 2001).
However, the timing at which such an electrical path or optical path is established is entrusted to the maintainer, and, since the amount of traffic which is transferred over the electrical path or the optical path is always varying, there is the problem that network resources may not always be efficiently utilized in accordance with the variations in the traffic.
In other words, the maintainer decides whether or not the data which is to transmitted from now on is single shot type data for which the amount of data is relatively small, or is burst type data for which the amount of data is relatively large, and establishes an electrical path or an optical path based upon the results of this decision. Thus, in the case of single shot type data, the IP addresses of the packets are electrically read by each router, and the next stage router is selected and forwarding is performed according to their IP addresses. Furthermore, in the case of burst type data, a cut through path is established between optical cross-connects or optical routers, and the packets are all forwarded together upon this cut through path without their IP addresses being electrically read.
It is anticipated that, by changing between an electrical path or an optical path according to this type of command from the maintainer, network resources will be efficiently taken advantage of by forwarding burst type data of which the quantity is relatively great at high speed, but it would be possible to anticipate even more efficient utilization of network resources, if it were possible to perform changing between an electrical path and an optical path automatically, based upon the results of actual observation of the amount of traffic which was varying moment by moment. However, no such proposal has as yet been presented.